DOCTOR of PHILOSOPHY Unravelling the Nature of Hydrogen

DOCTOR OF PHILOSOPHY Unravelling the nature of hydrogen-poor thermonuclear supernovae Magee, Mark Award date: 2019 Awarding institution: Queen's University Belfast Link to publication Terms of use All those accessing thesis content in Queen’s University Belfast Research Portal are subject to the following terms and conditions of use • Copyright is subject to the Copyright, Designs and Patent Act 1988, or as modified by any successor legislation • Copyright and moral rights for thesis content are retained by the author and/or other copyright owners • A copy of a thesis may be downloaded for personal non-commercial research/study without the need for permission or charge • Distribution or reproduction of thesis content in any format is not permitted without the permission of the copyright holder • When citing this work, full bibliographic details should be supplied, including the author, title, awarding institution and date of thesis Take down policy A thesis can be removed from the Research Portal if there has been a breach of copyright, or a similarly robust reason. 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Oct. 2021 Unravelling the nature of hydrogen-poor thermonuclear supernovae A thesis submitted for the degree of Doctor of Philosophy by Mark Richard Magee, MSci (Queen’s University Belfast 2014) Faculty of Engineering and Physical Sciences School of Mathematics and Physics Queen’s University Belfast Belfast, Northern Ireland, UK March 2018 Acknowledgements There are many people that I wish to thank and without whom I would not be here. First, I would like to thank my family. Thank you Mum for everything you’ve given me and everything you’ve sacrificed for me. Thank you Steph, Pat, Carmel, Gerardine, and Sean, for always believing that I could do this. Thank you Emma for encouraging me all of the times that I doubted myself, for the fun we’ve had these past years, and for putting up with me. Thank you Stephen, Cosimo, Anders, Kate, Mattia, Joe, Janet, and every other member of the supernova group, for fostering an environment in which I can learn and grow, for your help throughout the years, and for making my time as a PhD student enjoyable. Thank you Morgan for giving me my first experience of astronomy research and helping to start me on the journey leading to this point and beyond. Finally, I must thank my supervisors, Rubina and Stuart. My vocabulary is insuf- ficient to describe the depth of my respect, admiration, and gratitude for both of you. There is no doubt in my mind that the work I have accomplished during this thesis would not have been possible without your supervision. Having both of you as supervisors has made this the perfect PhD for me and I would not have it any other way. I could not imagine having anyone else for supervisors and I hope the past few years have been as fun and interesting for you as they have for me. You have both always been there to spend countless hours with me, answering questions, guiding me, and supporting me. Thank you for always pushing me to do more, to be a better scientist, and for giving me something to which I can aspire. M. R. Magee March 28, 2018 i Abstract Thermonuclear supernovae take many forms, as demonstrated by the increasing evi- dence of diversity among type Ia supernovae, particularly at early times, and subclasses of peculiar objects. This thesis presents new observations and modelling tools that ex- plore the diversity of thermonuclear supernovae. We present colour light curves, and optical and near-infrared spectra for SN 2015H, a type Iax supernova, beginning a few days post-explosion. We compare these observations to synthetic light curves and spectra predicted from multi-dimensional explosion models invoking weak deflagrations of Chandrasekhar-mass carbon-oxygen white dwarfs, and find reasonable agreement with 56 a model producing only ∼0.07 M of Ni. Our results demonstrate that the obser- vational signatures of this explosion scenario are consistent with type Iax supernovae across a range of luminosities. Our analysis of SN 2015H shows that the strength of the deflagration, and hence amount of 56Ni produced during the explosion, can explain some of the diversity observed among type Iax supernovae. In a subsequent study, we present observations of PS1-12bwh that demonstrate this is not the sole factor affect- ing the appearance of type Iax supernovae. While the light curve and post-maximum spectra of PS1-12bwh are virtually identical to the prototypical SN 2005hk, the pre- maximum spectrum of the former does not resemble spectra of the latter at a compara- ble epoch. We perform spectral modelling and find that the unique pre-maximum appearance of PS1-12bwh is consistent with a lower density in the outer ejecta compared to SN 2005hk. Both objects showed similar light curve peaks and shapes, therefore our analysis indicates that there are additional factors responsible for the diversity of type Iax supernovae apart from the amount of 56Ni produced; hence, type Iax supernovae are not a one-parameter family. The early light curves of type Ia supernovae also dis- play diversity in their colours and shapes. We therefore present a new Monte Carlo radiative transfer code designed for modelling light curves of radioactively driven tran- sients. We perform a parameter study, focusing on the effects of the 56Ni distribution and density profile within the supernova ejecta. Models with 56Ni extending throughout the entire ejecta show brighter and bluer light curves at early times. The density profile also plays a significant role in shaping the early light curve; however, this has been neglected in previous studies. Our models show that comparisons with full colour light curves are necessary to constrain the ejecta properties of type Ia supernovae, such as 56Ni distribution and density profile. ii Contents Acknowledgementsi Abstract ii List of tables vi List of figures viii List of abbreviations ix Publicationsx 1 Introduction1 1.1 Type Ia supernovae............................2 1.1.1 Light curves...........................4 1.1.2 Spectra..............................7 1.2 Peculiar type Ia supernovae........................9 1.3 Type Iax supernovae........................... 11 1.3.1 Light curves........................... 12 1.3.2 Spectra.............................. 13 1.3.3 Progenitors & Remnants..................... 15 1.4 Explosion models............................. 16 1.4.1 Chandrasekhar mass explosions................. 16 1.4.2 Sub-Chandrasekhar mass explosions............... 20 1.4.3 Core collapse........................... 23 1.5 Summary................................. 26 2 Data reduction 27 2.1 Imaging.................................. 28 2.1.1 Optical reduction......................... 28 2.1.2 Near-infrared reduction...................... 29 2.1.3 Photometry with SNOoPY.................... 30 iii 2.2 Spectroscopy............................... 33 3 Monte Carlo radiative transfer 39 3.1 Random sampling............................. 40 3.2 Photon redshifting............................. 42 3.3 The Sobolev approximation........................ 43 3.4 Expansion opacities............................ 44 3.5 General overview of the code....................... 45 3.6 Model set-up............................... 46 3.7 Packet initialisation............................ 47 3.8 Packet propagation............................ 48 3.8.1 Numerical events......................... 48 3.8.2 Physical events.......................... 50 3.9 Updates to the plasma state........................ 52 3.10 TARDIS.................................. 52 4 SN 2015H: Type Iax supernovae as pure deflagrations 57 4.1 Introduction................................ 58 4.2 Discovery................................. 59 4.3 Observations & Data Reduction..................... 59 4.3.1 Optical & near-IR imaging.................... 60 4.3.2 Optical & near-IR spectroscopy................. 63 4.4 Analysis.................................. 63 4.4.1 Reddening............................ 63 4.4.2 Photometry............................ 64 4.4.3 Spectroscopy........................... 71 4.5 Comparison with SN 2002cx and SN 2005hk.............. 75 4.6 Comparison to Deflagration Models................... 77 4.7 Summary................................. 80 Appendices 83 4.A Tables................................... 83 4.B Example TARDIS model for SN 2015H................. 90 5 PS1-12bwh: Additional diversity among type Iax supernovae 93 5.1 Introduction................................ 94 5.2 Observations & Data Reduction..................... 95 5.3 Analysis.................................. 100 5.3.1 Reddening............................ 100 5.3.2 Photometry............................ 100 iv 5.3.3 Spectroscopy........................... 101 5.4 Discussion................................. 106 5.4.1 Epoch misidentification..................... 106 5.4.2 Existing explosion models...................

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